共查询到20条相似文献,搜索用时 15 毫秒
1.
Thommy Ekström Lena K. L. Falk Zhi-Jian Shen 《Journal of the American Ceramic Society》1997,80(2):301-312
Duplex αβ,-sialon ceramics with a minimum volume fraction of residual intergranular glass have been prepared using Dy or Sm as the α-sialon stabilizing element. These microstructures contained high aspect ratio β-sialon grains homogeneously distributed in an α-sialon matrix. A number of the larger α-sialon grains contained dislocations and showed a core/shell structure. Dy gave an α-sialon which was stable over a wide temperature range (1350–1800°C) for long holding times, while the use of Sm resulted in less stable α-sialon structures at medium temperatures (1450°C) and the formation of melilite, R2 Si3−x Alx O3+x N4−x , β-sialon, and the 21R sialon polytype during prolonged heating. High α-phase contents gave a very high hardness ( H V10 is approximately 22 GPa) but a comparatively low indentation fracture toughness (around 4.4 MPam1/2 ). Duplex sialons fabricated from powder mixtures corresponding to an α-to-β sialon ratio of around 50:50 resulted in a sialon material with a favorable combination of high hardness (around 22 GPa) and increased toughness (to around 5.5 MPam1/2 ). 相似文献
2.
Mark I. Jones Hideki Hyuga Kiyoshi Hirao Yukihiko Yamauchi 《Journal of the American Ceramic Society》2004,87(4):710-713
α-SiAlONs with equiaxed and elongated microstructures stabilized with Y2 O3 and Lu2 O3 were produced by hot pressing, and the phase structure and room- and high-temperature mechanical properties were assessed. Additional liquid added to the starting composition in the form of 5 wt% rare-earth monosilicate resulted in the formation of elongated microstructures and improvements in room-temperature strength and fracture toughness. The elongated grain growth was promoted by the additional liquid phase, which crystallized to form a secondary grain-boundary phase thought to be J ' (Re4 Si2– x Al x O7+ x N2– x ). For the equiaxed and the elongated samples, those sintered with Lu2 O3 showed higher hardness than the comparable Y2 O3 -sintered materials, and, at elevated temperature, the strength retention of the elongated Lu2 O3 SiAlON was much higher than that of the Y2 O3 sample, which was attributed to properties of the residual grain-boundary phase associated with the difference in the cationic radius of the stabilizing cation. 相似文献
3.
Dense sialon ceramics along the tie line between Si3 N4 and Nd2 O3 ·9AlN were prepared by hot-pressing at 1800°C. The materials were subsequently heat-treated in the temperature range 1300–1750°C and cooled either by turning off the furnace (yielding a cooling rate (Tcool ) of ∼50°C/min) or quenching (Tcool ≥ 400°C/min). It was found necessary to use the quenching technique to reveal the true phase relationships at high temperature, and it was established that single-phase α-sialon forms for 0.30 x 0. 51 in the formula Ndx Si12–4S x Al4.5 x O1. 5 x , N16–1.5 x . The α-sialon is stable only at temperatures above 1650°C, and it transforms at lower temperatures by two slightly different diffusion-controlled processes. Firstly, an α-sialon phase with lower Nd content is formed together with an Al-containing Nd-melilite phase, and upon prolonged heat treatment thus-formed α-sialon decomposes to the more stable β-sialon and either the melilite phase or a new phase of the composition NdAl(Si6-z Alz )N10-z Oz . Nd-doped α-sialon ceramics containing no crystalline intergranular phase show very high hardness (HV10 = 22. 5 GPa) and a fracture toughness ( K lc = 4.4 MPa·m1/2 ) at room temperature. The presence of the melilite phase, which easily formed when slow cooling rates were applied or by post-heat-treatment, reduced both the fracture toughness and hardness of the materials. 相似文献
4.
Michael K. Cinibulk Gareth Thomas Sylvia M. Johnson 《Journal of the American Ceramic Society》1992,75(8):2050-2055
The flexural strength and creep behavior of RE2 Si2 O7 –Si3 N4 materials were examined. The retention in room-temperature strengths displayed by these ceramics at 1300°C was 80–91%, with no evidence of inelastic deformation preceding failure. The steady-state creep rates, at 1400°C in flexural mode, displayed by the most refractory materials are among the lowest reported for sintered Si3 N4 . The creep behavior was found to be strongly dependent on residual amorphous phase viscosity as well as on the oxidation behavior of these materials. All of the rare-earth oxide sintered materials, with the exception of Sm2 Si2 O7 –Si3 N4 , had lower creep strains than the Y2 Si2 O7 –Si3 N4 material. 相似文献
5.
Feng Ye Michael J. Hoffmann Stefan Holzer Yu Zhou Mikio Iwasa 《Journal of the American Ceramic Society》2003,86(12):2136-2142
The yttrium–sialon ceramics with the composition of Y0.333 Si10 Al2 ON15 and an excess addition of Y2 O3 (2 or 5 wt%) were fabricated by hot isostatic press (HIP) sintering at 1800°C for 1 h. The resulting materials were subsequently heat-treated in the temperature range 1300–1900°C to investigate its effect on the α→β-sialon phase transformation, the morphology of α-sialon grains, and mechanical properties. The results show that α-sialons stabilized by yttrium have high thermal stability. An adjustment of the α-sialon phase composition is the dominating reaction in the investigated Y–α-sialon ceramics during low-temperature annealing. Incorporation of excess Y2 O3 could effectively promote the formation of elongated α-sialon grains during post-heat-treating at relatively higher temperature (1700° and 1900°C) and hence resulted in a high fracture toughness ( K IC = 6.3 MPa·m1/2 ) via grain debonding and pullout effects. Although the addition of 5 wt% Y2 O3 could promote the growth of elongated α grains with a higher aspect ratio, the higher liquid-phase content increased the interfacial bonding strength and therefore hindered interface debonding and crack deflection. The heat treatment at 1500°C significantly changed the morphology of α-sialon grains from elongated to equiaxed and hence decreased its toughness. 相似文献
6.
Ya-Wen Li Pei-Ling Wang Wei-Wu Chen Yi-Bing Cheng Dong-Sheng Yan 《Journal of the American Ceramic Society》2002,85(10):2545-2549
Two calcium-doped α-SiAlON compositions (Ca0.6 Si10.2 Al1.8− O0.6 N15.4 and Ca1.8 Si6.6 Al5.4 O1.8 N14.2 ) were prepared by hot pressing at 1600° and 1500°C, respectively, for complete phase transformation from α-Si3 N4 to α-SiAlON. Both samples were subsequently fired at different temperatures for different periods of time to study the grain growth of α-SiAlON. Elongated α-SiAlON grains were developed in both samples at high temperatures. The kinetics of grain growth was investigated based on the variations in length and width of the α-SiAlON grains under different sintering conditions. Different growth rates were found between the length and width directions of the α-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development. 相似文献
7.
Mamoru Mitomo Yoh-ichiro Sato Nobuo Ayuzawa Isamu Yashima 《Journal of the American Ceramic Society》1991,74(4):856-858
Plasma etching of β-Si3 N4 , α-sialon/β-Si3 N4 and α-sialon ceramics were performed with hydrogen glow plasma at 600°C for 10 h. The preferential etching of β-Si3 N4 grains was observed. The etching rate of α-sialon grains and of the grain-boundary glassy phase was distinctly lower than that of β-Si3 N4 grains. The size, shape, and distribution of β-Si3 N4 grains in the α-sialon/β-Si3 N4 composite ceramics were revealed by the present method. 相似文献
8.
A significant solubility of Al in N-melilite phases (M) has been observed, and this results in the formation of a melilite solid solution (M'ss ) of general formula Ln2 Si3 − x Al x O3 + x N4 − x (Ln = rare earth). Up to one Si can be replaced by Al without change of structure, and the M'solid solution terminates at Ln2 Si2 AlO4 N3 in samarium SiAlON systems. M'ss may appear as an intermediate phase during the sintering of SiAlONs, and its melting temperature is critical to the densification of the materials. For example, samarium M'ss melts at a temperature lower than neodymium M'ss , and as a result, samarium oxide shows better densification behavior in the preparation of α-SiAION ceramics than does neodymium oxide. Devitrification of M'ss from an amorphous grain boundary phase occurs above 1500°C during post heat-treatment. The M'ss is refractory and may offer better oxidation resistance than N-melilite because of the replacement of Al─O for Si─N in the structure. Therefore M'ss , is considered to be a most desirable grain boundary phase for α and α–β SiAlON ceramics. 相似文献
9.
Crystallizing the grain-boundary glass of a liquid-phase-sintered Si3 N4 ceramic for 2 h or less at 1500° led to formation of δ-Y2 Si2 O7 . After 5 h at 1500°, the δ-Y2 Si2 O7 had transformed to β-Y2 Si2 O7 with a concurrent dramatic increase in dislocation density within β-Si3 N4 grains. Reasons for the increased dislocation density are discussed. Annealing for 20 h at 1500° reduced dislocation densities to the levels found in as-sintered material. 相似文献
10.
Thommy Ekström Harald Herbertsson Matthew James Ian Fleck 《Journal of the American Ceramic Society》1994,77(12):3087-3092
β-sialon and Nd2 O3 -doped α-sialon materials of varying composition were prepared by sintering at 1775° and 1825°C and by glass-encapsulated hot isostatic pressing at 1700°C. Composites were also prepared by adding 2–20 wt% ZrO2 (3 mol% Nd2 O3 ) or 2–20 wt% ZrN to the β-sialon and α-sialon matrix, respectively. Neodymium was found to be a fairly poor α-sialon stabilizer even within the α-phase solid solution area, and addition of ZrN further inhibited the formation of the α-sialon phase. A decrease in Vickers hardness and an increase in toughness with increasing content of ZrO2 (Nd2 O3 ) or ZrN were seen in both the HIPed β-sialon/ZrO2 (Nd2 O3 ) composites and the HIPed Nd2 O3 -stabiIized α-sialons with ZrN additions. 相似文献
11.
Silicon nitride (Si3 N4 ) ceramics, prepared with Y2 O3 and Al2 O3 sintering additives, have been densified in air at temperatures of up to 1750°C using a conventional MoSi2 element furnace. At the highest sintering temperatures, densities in excess of 98% of theoretical have been achieved for materials prepared with a combined sintering addition of 12 wt% Y2 O3 and 3 wt% Al2 O3 . Densification is accompanied by a small weight gain (typically <1–2 wt%), because of limited passive oxidation of the sample. Complete α- to β-Si3 N4 transformation can be achieved at temperatures above 1650°C, although a low volume fraction of Si2 N2 O is also observed to form below 1750°C. Partial crystallization of the residual grain-boundary glassy phase was also apparent, with β-Y2 Si2 O7 being noted in the majority of samples. The microstructures of the sintered materials exhibited typical β-Si3 N4 elongated grain morphologies, indicating potential for low-cost processing of in situ toughened Si3 N4 -based ceramics. 相似文献
12.
Jiuxin Jiang Bo Zhu Peiling Wang Weiwu Chen Dongsheng Yan Hanrui Zhuang Yibing Cheng 《Journal of the American Ceramic Society》2005,88(4):950-953
The Pr α-sialon powders prepared by self-propagating high-temperature synthesis (SHS), consisting of 55 wt% Pr α-sialon and 45 wt% of β-sialon (abbreviated as α' and β'), were hot-pressed at 1800°C for 1 h. The results showed that Pr α' phase would transfer to β' with the appearance of JEM phase (Pr(Si6− z Al z )(N10− z O z )) after sintering, thus resulting in the increase of β' phase to 86 wt%. The addition of Y2 O3 into SHS-ed Pr α' powders as the starting materials restrains the transformation of α' to β' and prevents the formation of JEM phase as well. The nucleation mechanism of Pr α' grain during hot-pressing was investigated in terms of transmission electron microscope and energy-dispersive spectrometer analysis. Two nucleation modes of Pr α' grains were found, i.e., nucleating on the undissolved Pr α' grains and on the nuclei of (Pr, Y) α' grains precipitated from liquid phase. 相似文献
13.
Rong-Jun Xie Naoto Hirosaki Mamoru Mitomo Yoshinobu Yamamoto Takayuki Suehiro Naoki Ohashi 《Journal of the American Ceramic Society》2004,87(7):1368-1370
Cerium-doped α-SiAlON (M x Si12−( m + n ) Al m + n O n N16– n ) materials have been prepared by gas-pressure sintering and post-hot-isostatic-press (HIP) annealing, using four powder mixtures of α-Si3 N4 , AlN, and either (i) CeO2 , (ii) CeO2 + Y-α-SiAlON seed, (iii) CeO2 + Y2 O3 , or (iv) CeO2 + CaO. Cerium-containing CeAl(Si6– z Al z )(N10– z O z ) (JEM) phase, rather than Ce-α-SiAlON phase, forms in the sample with only CeO2 , whereas a single-phase α-SiAlON generates in samples with dual doping (CeO2 + Y2 O3 and CeO2 + CaO). On ultraviolet-light excitation, JEM gives one broad emission band with maximum at 465 nm and a shoulder at 498 nm; α-SiAlON shows an intense and broad emission band that peaks at 500 nm. The unusual long-wavelength emissions in JEM and α-SiAlON are due to increases in the nephelauxetic effect and the ligand-field splitting of the 5 d band, because the coordination of Ce3+ in JEM and α-SiAlON is nitrogen enriched. 相似文献
14.
Elongated β'-SiAlON grains grown from several finegrained Ym/3 Si12(m+n) Alm+n On N16–r compositions with α-Si3 N4 , AlN, Al2 O3 , and Y2 O3 starting materials have been examined. These grains have large aspect ratios and are oriented along the [0001] axis. TEM structural and chemical analysis suggests that they are nucleated from various seed crystals, which can be α-Si3 N4 , β-Si3 N4 , or other β'-SiAlON. The β'-SiAlON seed and the initial precipitation on β-Si3 N4 show a higher content of Al and O, indicating that a large transient supersaturation of Al and O in the liquid is instrumental for β'-SiAlON formation, whereas subsequent growth proceeds under a much lower driving force. The misfit between phases is accommodated by interfacial dislocations ( c -type and a -type). Fully grown β'-SiAlON grains usually contain several variants independently nucleated from the same seed. In particular, the two alternative α/β phase-matching possibilities result in two [0001] growth habits separated by a twin boundary. 相似文献
15.
Naoto Hirosaki Yoshinobu Yamamoto Toshiyuki Nishimura Mamoru Mitomo Junichi Takahashi Hisanori Yamane Masahiko Shimada 《Journal of the American Ceramic Society》2002,85(11):2861-2863
Phase relationships in the Si3 N4 –SiO2 –Lu2 O3 system were investigated at 1850°C in 1 MPa N2 . Only J-phase, Lu4 Si2 O7 N2 (monoclinic, space group P 21 / c , a = 0.74235(8) nm, b = 1.02649(10) nm, c = 1.06595(12) nm, and β= 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si3 N4 –SiO2 –Lu2 O3 system. The Si3 N4 /Lu2 O3 ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu–J-phase, β-Si3 N4 , and a new phase of Lu3 Si5 ON9 , having orthorhombic symmetry, space group Pbcm (No. 57), with a = 0.49361(5) nm, b = 1.60622(16) nm, and c = 1.05143(11) nm. The new phase is best represented in the new Si3 N4 –LuN–Lu2 O3 system. The phase diagram suggests that Lu4 Si2 O7 N2 is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications. 相似文献
16.
Wei-Ying Sun Tseng-Ying Tien Tung-Sheng Yen 《Journal of the American Ceramic Society》1991,74(10):2547-2550
The solubility limit of α'-SiAION solid solutions on the Si3 N4 ─YN:3AIN composition join in the system Si3 N4 ─YN─AIN has been determined at 1800°C. The end members of these solid solutions are Y0.43 Si10.7 Al1.3 N16 and Y0.8 Si9.6 Al2.4 N16 . Unit-cell dimensions of the α'-SiAION solid solutions in the system Si,Al,Y/N,O can be expressed as follows: a o (Å) = 7.752 + 0.045 m + 0.009 n , c o (Å) = 5.620 + 0.048 m + 0.009 n , where the α'-SiAION solid solution has the formula Y x Si12-( m+n ) Al m+n N16- n O n . The single-phase boundary of the solid solution α'-SiAION on the composition triangle Si3 N4 ─YN:3AIN─AIN:Al2 O3 is delineated. The present paper also reports the phase relationships involving α'-SiAION. 相似文献
17.
Michael K. Cinibulk Gareth Thomas Sylvia M. Johnson 《Journal of the American Ceramic Society》1990,73(6):1606-1612
Densifying silicon nitride with a YSiAlON glass additive produced 99% dense materials by pressureless sintering. Subsequent heat-treating led to nearly complete crystallization of the amorphous intergranular phase. Transmission electron microscopy revealed that for heat treatments at 1350°C, only β-Y2 Si2 O7 was crystallized at the grain boundaries. At a higher temperature of 1450°C, primarily YSiO2 N and Y4 Si2 O7 N2 in addition to small amounts of Y2 SiO5 were present. Al existed only in high concentrations in residual amorphous phases, and in solid solution with Si3 N4 and some crystalline grain-boundary phases. In four-point flexure tests materials retained up to 73% of their strengths, with strengths of up to 426 MPa, at 1300°C. High-strength retention was due to nearly complete crystallization of the intergranular phase, as well as to the high refractoriness of residual amorphous phases. 相似文献
18.
Xinwen Zhu Tohru S. Suzuki Tetsuo Uchikoshi Yoshio Sakka 《Journal of the American Ceramic Society》2008,91(2):620-623
This paper reports the texturing behavior of β-sialon by strong magnetic field alignment (SMFA) during slip casting, followed by reaction pressureless sintering, using either α or β-Si3 N4 , Al2 O3 , and AlN as the starting materials. It is found that the β-Si3 N4 crystal exhibits a substantially stronger orientation ability than the α-Si3 N4 crystal regardless of the Si3 N4 raw powders in the magnetic field of 12 T. The β-raw powder produces a highly a , b -axis-oriented β-Si3 N4 green body with a Lotgering orientation factor of up to 0.97. During sintering, the β-raw powder allows the a , b -axis-oriented β-sialon to retain the Lotgering orientation factor similar to and even higher than that of β-Si3 N4 in the green body. In contrast, the α-raw powder leads to a faster transformation rate of α/β-Si3 N4 to β-sialon but a substantially lower texture in β-sialon. The results indicate that the use of the β-raw powder is more efficient for producing highly textured β-sialon via SMFA than that of the α-raw powder as well as the prolonged sintering. 相似文献
19.
A novel porous Yb4 Si2 O7 N2 material with uniform open-cell network structure was fabricated from the reaction between Si3 N4 , Yb2 O3 , and SiO2 . The formation of Yb4 Si2 O7 N2 during heating was studied using X-ray diffractometry. The porous structure was characterized using scanning electron microscopy and mercury porosimeter. It is shown that the formation of Yb4 Si2 O7 N2 phase starts at ∼1150°C and completes at 1350°C for 4 h, accompanied by the development of open-cell network structure. The necks between Yb4 Si2 O7 N2 particles become much thicker with increasing temperature because of the coarsening of Yb4 Si2 O7 N2 particles, thus leading to a uniform three-dimensional network structure. Furthermore, the pore size can be well controlled by adjusting reacting temperature and altering atmosphere. 相似文献
20.
The subsolidus phase diagram of the quasiternary system Si3 N4 -AlN-Y2 O3 was established. In this system α-Si3 N4 forms a solid solution with 0.1Y2 O3 : 0.9 AIN. The solubility limits are represented by Y0.33 Si10.5 Al1.5 O0.5 N15.5 and Y0.67 Si9 A13 ON15 . At 1700°C an equilibrium exists between β-Si3 N4 and this solid solution. 相似文献